Organic electroluminescence (referred to as “organic EL” hereinafter) is expected to be applied as surface emission to main lighting and liquid crystal display backlight. A common organic EL device has a multi-layer structure composed of a transparent substrate, a transparent electrode, a light-emitting layer, and a reflecting electrode. Light from a light-emitting source (light-emitting layer) travels through the transparent electrode and the transparent substrate, is output from the atmosphere-facing surface of the transparent substrate, and is thus extracted to the atmosphere (the outside of the organic EL device). Specifically, due to the difference in refractive index between the transparent substrate and the transparent electrode, about 45% of the light is lost by total reflection at the interface between the transparent substrate and the transparent electrode (substrate-transparent electrode interface) in the form of light propagated in the transparent electrode or light propagated laterally along the substrate-transparent electrode interface. This phenomenon is one of the major factors for low efficiency in the extraction of emitted light to the outside. Various attempts have been conventionally made to avoid such a phenomenon and thus increase the efficiency in the extraction of light from the exposed surface (atmosphere-facing surface) of the transparent substrate.
In general, ITO (Indium Tin Oxide) has been used in transparent electrodes for use in organic EL devices. Recently, however, ultrafine metal fibers such as metal nanofibers and metal nanowires have often been used in transparent electrodes as an alternative to ITO which is a rare metal and the depletion of whose source is causing concern. Various methods have been proposed as methods for patterning transparent electrodes in which such ultrafine metal fibers are used. For example, a patterning method is known in which a transparent electrode containing ultrafine metal fibers is formed on a surface of a transparent substrate, and unnecessary portions are removed by photoetching or laser processing to form non-conductive regions (Patent Literature 1 to 3).